Watershed Management: Protecting Our Groundwater

by Carolyn Boda and Alison Marczak

INTRODUCTION

Water quality is a reflection of its watershed and the actions that take place on the watershed. A watershed is a geographic area in which water, sediments, and dissolved materials drain to a common outlet such as a stream, lake, aquifer, estuary, or an ocean. It is a system--a functioning unit with interacting biological, physical, chemical, and human components. As water flows through the watershed, it picks up chemical and physical characteristics from the land over which it flows. The chemical and physical composition of this runoff directly affects the water quality of the receiving water body. If you know the watershed you live in, you will know which receiving body of water is affected by your property management decisions. To learn about which watershed you live in check out Surf Your Watershed http://www.epa.gov/surf/

WATERSHED CONTAMINATION OVERVIEW

The influence that people and urbanization have upon a watershed is a large factor in its health and maintenance. Activities such as building construction, improper waste disposal, and neglected septic tank maintenance can all contaminate the watershed and the drinking water supplies it serves. These water supplies include groundwater, lakes, and reservoirs. Pollutants in the watershed can leak down into the groundwater causing contamination, which is difficult and often impossible to identify and remediate. Lakes and reservoirs must be strickly monitored to determine if contaminants have entered its source. Contaminated water not only affects people but also those animals that rely on clean water supplies. There are two types of pollution that affect water supplies. The first type is point source (PS) which includes septic tanks, leaking underground storage tanks (LUST), and landfills. The second type is non-point source (NPS), which includes run-off from impervious surfaces and agricultural activities. We have chosen to discuss only these sources out of the many that can have an adverse effect on the watershed. Point and non-point source pollution are becoming severe problems as urbanization continues to increase. With safe monitoring practice and watershed education to the public, pollution problems can be greatly reduced and possibly prevented.

Disposing of motor oil in puddle

Neglected leaking steel drum

SEPTIC TANKS

A septic tank is an underground sewage collection system. There are approximately 22 million septic systems in the United States which serve about 1/3 of the population. With a flow of about 49,000-75,000 gal/year, septic systems discharge 3.5 billion gallons of waste water per day (Gallagher,1997).

The tank itself is made of a very durable material which is resistant to corrosion or decay. The size of the tank needed for proper waste disposal is determined by the number of bedrooms in the house for which it will be used. The tank volume should allow for 24 hour fluid retention plus sludge accumulation at the bottom. A septic tank is designed to hold a certain amount of waste or sludge. A properly designed tank can hold sludge for up to three years, after which pumping should take place. If proper maintenance does not take place this sludge could accumulate so that it eventually overflows into the surrounding absorption areas (Gallagher,1997).

The absorption area is a field of perforated pipes set in trenches which are 1-3 feet wide and lined on the bottom with gravel or rock. Here discharged effluent water from the tank drains and percolates through the subsoil to the groundwater. This area is not designed to treat sludge and if overflow does occur, the groundwater could be contaminated leading to pollution of the watershed. Percolation rates are listed in the table below (Gallagher, 1997).

Leaking tanks may allow poisonous compounds such as nitrates and pathogens such as E.coli to enter the groundwater. Nitrates are toxic to humans, especially small infants, and may prevent the blood from carrying oxygen causing infant methemoglobin or blue babies. E.coli contamination can cause fatal diseases such as dysentery or hepatitis. E.coli is used as and indicator organism for septic tank contamination. If E.coli is found in drinking water supplies then the septic system needs to be inspected and repaired immediately.

Percolation Rates	Comments
5-60 min/inch	Acceptable
1-5 min/inch	Marginal (Too Fast)
60-120 min/inch	Marginal (Too Slow)
<1 or >120 min/inch	Unacceptable

Certain materials are extremely hazardous to groundwater if they are flushed into a septic system. Such materials are motor oil, gasoline, paint thinners, and pesticides. Heavily accumulated household cleaners are also toxic. Septic tank owners should have a knowledge of how to take proper care of their septic tanks. Septic systems should be checked annually for leaks and sludge appearing on the soil surface. A maintenance record should also be updated.

Septic Tank Installation

Installation of Absorption Field Trenches

Filling Trenches with Gravel

Photos by Daniel Gallagher

For more information concerning septic tank systems click here.

UNDERGROUND STORAGE TANKS

Underground storage tanks (USTs) are widely used throughout the nation to store petroleum products, chemicals, and other wastes. LUST’s are the main cause of groundwater contamination in the US, and the Environmental Protection Agency (EPA) has estimated that an average of 25% of the thousands of tanks that exist are leaking (Gallagher,1997).

UST’s are heavily regulated under RCRA and in 1988 standards as to the durability and overflow protection the tank must meet. There are an estimated 10,280 USTs and 2,500,000 liquid petroleum and nonhazardous waste USTs that need to be addressed at this point according to RCRA. Tanks installed prior to 1988 must meet corrosion protection and leak detection requirements. Most steel USTs leak because of corrosion, but according to an EPA report, less that half of gasoline contamination is actually due to leaking tanks but to poor management practices such as overfilling. Since the nation draws half of its drinking water from underground sources, these leaking tanks pose an enormous threat to health and safety. A major threat to groundwater in BTEX because of its high solubility and the fact that Benzene has been found to be a carcinogen (Gallagher,1997).

Corroding UST

RUN-OFF

Urbanization increases the amount of paved parking lots, sidewalks, and roads. These impervious surfaces result in increased rainwater run-off, which consequently carries with it any dirt or chemicals which have been dripped, spilled, or leaked onto the pavement. Whether the run-off eventually percolates into the ground or enters a nearby stream, the pollutants it is carrying will eventually reach and contaminate the groundwater.

Yellow booms used to collect construction sediments in drinking water reservoir

Run-off from agricultural activity is also a major cause of groundwater pollution. Excessive amounts of fertilizer and pesticides can wash off of the land and get carried into water supplies, contaminating them with nitrogen and phosphorous. Animal feeding operations can also fill the run-off with manure, food additives, nitrates, and antibiotics. To help prevent this agricultural run-off from entering nearby water systems, buffer zones are required. A buffer zone is a strip of land about wide around a farm which serves as an area for the run-off to infiltrate into the ground and biodegrade before it directly enters and pollutes the water system.

Run-off with its pollution and harmful effects can be reduced by limiting the amount of impervious surfaces. For instance, gravel can be used for driveways and parking lots instead of asphalt. Bricks and wood can be used for sidewalks instead of concrete slabs, and contractors can design neighborhoods with larger lots of land per house. All of these alleviate run-off and give the rainwater more time and space to infiltrate into the ground, where contaminants have a greater chance of being removed through adsorption and bioremediation. The slower the infiltration, the more time there is for the contaminants to adsorb onto the soil and biodegrade as a result of organisms within the soil. This type of remediation is natural, and greatly helps to cleanse the water of its contaminants before it reaches the groundwater.

Car wash run-off flowing into storm drain

Booms in contaminated ground water site

LANDFILLS

Landfills are a major factor in water pollution. Containing everything from oils to toxic chemicals, landfill leachate can be a large burden on a watershed. Careful measures and management practices are taken to prevent this leachate from contaminating the surrounding watershed.

Leachate is water which percolates through the soil layer and landfill removing soluble compounds in the disposed waste as it goes. It is for this reason that new landfills are required to have 2 or more liners and leachate collection systems above and between liners. Liners can be made of highly compacted clay and/or plastic which is non-permeable. Landfills should also be strategically located well above the water table in a soil with a low permeability so as to help prevent further seepage of the leachate. These soils usually have a very high clay content.

For more information concerning landfills click here.

CONCLUSION

All of these processes that take place in the watershed affect the quality of water supplies. One-half of the nations drinking water is supplied by groundwater aquifers which, in turn, are recharged from the watershed (Gallagher, 1997). It is very important that the groundwater supplies remain clean because they are very hard to monitor and remediate once contaminated. This is the reason the sources of PS and NPS pollution in the watershed must carefully be managed. Watershed management is the process of maintaining the quality of receiving waters by managing the quality and quantity of contributing surface and subsurface runoff through guidance and control of land use practices and development in the watershed. Environmental professionals and local citizens can both do their share to protect contamination of the watershed. Watershed inspectors, monthly hazardous material collections, and educational pamphlets are just a few examples of what is being done today to save our valuable water supplies.